1. Field of the Invention
The present invention relates to an automatic focusing apparatus comprising a camera having a distance measuring function through a TTL optical system, and a lens with a lens driving circuit for driving the lens in accordance with lens drive amount data supplied from the camera.
2. Description of the Prior Art
In a system of the type described above, the distance measurement data obtained during the lens drive operation does not accurately represent an actual distance. Therefore, the distance measuring operation must be prohibited during the lens drive operation. For this purpose, connecting terminals or contacts between the camera and the lens in this system must include a data line for transferring the lens drive amount data to the lens side, and another line for transferring to the camera a signal which represents that the lens is being driven and which is used to disable the distance measuring operation during the lens drive operation.
When the lens drive amount data is transferred in the form of a digital signal a data line having a large number of bits is required. For this reason, serial data transfer is adopted. However, in this case, sync clocks for serial data transfer must be supplied from the camera to the lens in addition to the lens drive amount data. This means that a minimum of three lines must be included, resulting in an increase in the number of contacts between the lens and the camera.
Various types of lenses can be used, including a lens having a distance measuring function, an AF lens or a normal lens in addition to the lens of the type described above. The camera must allow the mounting of any lens.
The AF lens performs automatic focusing. When this lens is mounted on the camera, the camera need not perform an operation to calculate a lens drive amount.
With a normal lens, even if a signal representing the lens drive amount is supplied from the camera, the lens cannot be driven. Then, the operation as described above need not be performed.